Revertion of changes related to ExternalShapeBase

This reverts commits:
50b60c5508b3ba5a0b8dc05eac511d7edaa5a343
0ae0301d1cd6e690473f932411ca880c20f45e13
2a594eb22bfed62fdbcef51a56c2c180bea0283f

Got some suggestions that the deleted things can be usefull.
Rename ExternalMediaShape to IExternalMediaShapeBase

"I" because of interface.
"Base" because it's an interface of a base class
and because it's easy to mix it up with the inherited MediaShape.
(MediaShape also an externally rendered thing so
the name ExternalMediaShape doesn't make any
difference between the two classes)

Change-Id: I4a03dd090034092942eea39d35894ce6cfc9947b